The retrofitting methods according to the known art, fundamentally propose the mere substitution of the internals within the shell, in particular of the pre-existing catalytic bed or beds, with new radial or axial-radial high-yield beds.
Although these modernization methods allow to obtain, on the one hand, an increase of the reactor production capacity and/or conversion yield while maintaining the external structure thereof unaltered, they fail on the other hand to attain a recovery at an increased thermal level of the heat generated during the synthesis reaction.
In almost all cases, in fact, the reactor gas outlet nozzle is not able to withstand the temperature of the reaction gases leaving the lowermost catalytic bed, up to the point that they must be cooled before being discharged to the outside.
The need of maintaining the external structure of the synthesis reactor unaltered therefore allows the known modernization methods only a recovery of the heat possessed by the reaction products to a limited thermal level, which recovery does not exceed a pre-heating of boiler feed water or production of low pressure steam (less than 40 bar).